In the treatment of wastewater, a sludge product is generated. As the resulting biosolids contain nutrient value as a soil amendment, and are disposed of by land application, there is a need to both reduce the number of pathogens in the solid, and to reduce its attraction of vectors (birds, flies, animals) that could transport pathogens to other locations. This problem of pathogen reduction has been the subject of numerous articles.
U.S. Pat. No. 5,281,341, entitled “Sludge Treatment Process” describes a method of treating a liquid waste or process stream that includes a sludge component and that enhances sludge treatment or stabilization. The sludge is acidified to a pH of less than 4.0 in an oxygen enriched environment. A nitrous acid level is maintained sufficiently high to kill pathogens, in a closed chamber so that the nitrous acid won't be lost from the chamber through volatilization. U.S. Pat. No. 5,281,341 is incorporated herein by reference.
U.S. Pat. No. 4,936,983, entitled “Sewage Sludge Treatment With Gas Injection,” relates to an apparatus for treating sewage sludge in a hyperbaric vessel in which the sludge is oxygenated by injecting an oxygen-rich gas into the sewage sludge and then dispersing the mixture of sludge and oxygen-rich gas into the upper portion of a hyperbaric vessel for further interaction with an oxygen-rich atmosphere. The oxygen-rich gas is injected into the sewage sludge by delivering the gas to a combination gas and sludge mixing and dispersing assembly. This patent teaches a process to stabilize municipal sludge by acidifying the sludge to a pH of between 2.5 and 3.5 in the presence of 200 to 300 ppm (parts per million) of oxygen at a pressure of 60 psi and a pure oxygen stream containing 3.0% to 6.0% ozone for a period of 30–90 minutes. The process was ineffective against viruses and Ascaris eggs. These data indicate PSRP and PFRP inactivation criteria being met for bacteria only. U.S. Pat. No. 4,936,983 is hereby incorporated herein by reference in its entirety.
The problem of disinfection and stabilization of municipal and agricultural wastes is global. The present invention teaches a method that offers significant performance and economic advantages over known methods to make the treatment of this material practical for both municipalities and agricultural operations.